Think of zones as waypoints on an animals programmed daily pathway. So you're going to have to test all the theories for yourself anyway. Males spawn as males, females spawn as females. If there was even a tiny chance that males could spawn as females, the maps would be overrun by females. Many players (myself included) harvest almost only males. Harvested animals spawn as the same gender, with a small chance of being bigger or smaller and a greater chance of remaining the same. Oh, and you don't need to balance male/female ratio.
The reason the Youtubers get so many diamonds, is that A) They spend A LOT of time playing and B) They know all the need zones for particular animals and move from multiplayer server to multiplayer server, efficiently checking out the good spots, thus increasing their chances of finding a diamond. Which you wouldn't, because there would be no animals to spot in the need zones, since they hadn't spawned.
If active need zones were necessary for spawning, then there would be no animals on the maps until you'd found one. It's because a lot of people like to pretend that the game is deeper and more complex than it really is.
